Yes. His on/off numbers are insane.
Since they got Durant, the Warriors have only played 189 minutes (397 possessions) with Steph on the court and without any of the big 3 (Klay, Dray, and Durant) together. In those 189 minutes, the Warriors have a net rating of +17.3 per 100 possessions.
If you swap it, the other big 3 have played 1,493 possessions together without Steph, those possessions have a net rating of +2.8. Now granted, the sample size on the Steph minutes without those 3 is crazy low, and probably consists of blowouts, so take it for what it's worth. But the crazier thing is that when the big 3 play without Steph, they are just +2.8.
Meanwhile, some of the other 3 man combos
Steph/Durant/Dray and no Klay: (682 possessions) +13.9
Steph/Dray/Klay and no KD (1,551 possessions) +16.2
Steph/Durant/Klay and no Dray (915 possessions) +12.5